The present invention is directed to a filter system for filtering water and/or wastewater. More particularly, the present invention is directed to a modular filter system for filtering water and/or wastewater.
Modular filter systems, i.e., filter systems having a plurality of filter compartments or cells rather than a single large filter bed for a given filter unit, were primarily developed to reduce the size and complexity of the backwash or cleaning structure of single, large filter beds as well as obviate the need for a total system shutdown during the backwash or cleaning procedure. One such modular filter system is disclosed in U.S. Pat. No. 4,308,141 (xe2x80x9c""141 patent) the entire contents of which are incorporated herein by reference.
The ""141 patent discloses a filter system that utilizes a tank or reservoir having a transversely positioned porous filter element vertically spaced above the floor or bottom of the reservoir. Wall partitions are used to divide the tank into a plurality of smaller individual compartments or cells that have a common underdrain and plenum chamber. Influent or water containing undesired suspended particulate matter is introduced into the reservoir to filter the same. Gravity causes the influent to pass through the media in each of the cells or compartments. The filtered water or effluent is drawn away by a drain or effluent discharge located beneath or in the lower portion of the filter that communicates with the common plenum.
After a period of time of operating the modular filter system of the ""141 patent to filter influent, the system requires cleaning or backwashing to remove the particulate matter collected in the media contained in the individual cells. The ""141 patent teaches sequentially backwashing or cleaning each of the individual cells. Because the cells are backwashed sequentially, the filter system never needs to be shutdown for a backwash or filter cleaning cycle and all of the filter cells except the one being cleaned are operable continuously.
The backwash system of the ""141 patent includes a hydraulically isolating, backwash hood assembly and associated mobile carriage and platform support assembly. The backwash hood assembly depends from the mobile carriage and platform assembly and is initially centered over one of the six individual cells. Subsequently, the hood assembly is lowered to form a watertight seal with a particular cell to be backwashed. A backwash pump is activated creating a negative pressure within the backwash hood. Effluent created by adjacent individual cells is drawn up from the common underdrain through the media in the cell being backwashed to expand and wash the media. The effluent used to backwash a given cell is directed to waste through the hood assembly. This procedure is subsequently performed on all remaining individual cells.
In the commercial application of the ""141 patent, the effluent discharge is closed during the backwash procedure. Hence, all effluent from a given bank of cells having a common plenum during backwashing is directed to waste through the hood assembly. Once backwashing is complete, the effluent valve is opened thereby directing the effluent to a storage tank or other suitable location for storing filtered water.
Neither the ""141 patent or its commercial embodiment perform a filter to waste step for the last individual cell prior to opening the effluent valve. The ""141 patent does not disclose or suggest any structure for performing such a step. This is a significant draw back of the modular filter system disclosed in the ""141 patent. Without a filter to waste step performed on the last individual cell prior to opening the effluent discharge following backwashing, there exists a distinct possibility that the effluent will not be satisfactorily cleansed of undesirable impurities. Further, the suitably of the modular filter system of the ""141 patent and its commercial embodiment to filter water and wastewater is limited by regulations which require a filter to waste step. It should be noted that a filter to waste step is customarily performed in conventional filters, i.e., a filter having a single large filter bed per filter unit, when conventional filters are used in potable water applications. A filter to waste step includes passing fluid through a filter bed after backwashing but prior to opening the effluent discharge to ensure that any or at least most undesired impurities are removed from the filter bed prior to returning the filter system to its filtration mode.
The present invention overcomes the disadvantages of the ""141 patent and its commercial embodiment by providing a novel and unobvious method and apparatus for readily and inexpensively performing a filter to waste step on the last cell to be backwashed.
An object of the present invention is to provide a novel and unobvious modular filter system.
Another object of the present invention is to provide a modular filter system that overcomes one or more disadvantages of previously known modular filter systems.
A further object of the present invention is to provide a modular filter system with a mechanism for simply and inexpensively performing a filter to waste step or cycle following backwashing of the last cell of a multi-cell system.
Yet a further object of the present invention is to provide a modular filter system that avoids and/or reduces the possibility of the discharge of effluent having undesired impurities into a filtered water storage device or other location from which consumers obtain potable water.
It must be understood that no one embodiment of the present invention need include all of the aforementioned objects of the present invention. Rather, a given embodiment may include one or more of the aforementioned objects. Accordingly, these objects are not to be used to limit the scope of the claims of the present invention.
In summary, one embodiment of the present invention is directed to a modular filter system having a mechanism for performing a filter to waste step on the last cell of a multi-cell system following backwashing. Another embodiment of the present invention is directed to a method of operating a modular filter system in which a filter to waste step is performed on the last cell of a multi-cell system after backwashing.